The invention relates to a device for a hydraulic unit, in particular in anti-skid systems for vehicle brake systems.
Devices of this type are included in motor vehicle brake systems provided with anti-skid systems. The vehicle brake systems are mounted on the wheels of the vehicle and provided with brake pressure lines that lead to the hydraulic brake system. To generate brake pressure and hence braking action, a master brake cylinder is actuated with the aid of a foot pedal. In modern vehicles, anti-skid systems are additionally built in with which in anti-skid operation a braking pressure is likewise generated for an automatically adapted braking, which nevertheless prevents wheel locking. To this end, sensors are attached to the wheels to detect any danger of locking, or skidding, and via a control unit signals from the sensors act on a motor, a return pump and magnetic control valves, for example, and thus effect suitable pressure changes in the brake lines compared with the pressure of the master brake cylinder. In the process of pressure equalization at the master brake cylinder, pulsations are created that are perceptible to the driver at the foot pedal. The process produces irritating noises as well.
German Offenlegungsschrift 23 36 973 discloses a device of the above-mentioned type. In this known version of a radial piston fluid pump, a pump piston is forced with a drive side against an eccentric cam. The drive side of the pump piston is provided with a recess to receive a sliding body, which is defined in that it comprises an elastic plastic, that the height of the sliding body is greater than the depth of the recess, and that the sliding body is axially movable in the recess. This is intended to prevent the loud percussive noises that is produced by the pistons as they lift up from the cam race if the pilot pressure in such pumps fails. In the pumping strokes that occur, the sliding body is intended to elastically absorb the resultant impacts, both to prevent noise from being generated and to prevent undue strain on the cam race.
To prevent recoiling motion of the brake pedal, German Offenlegungsschrift 34 38 646 proposes a device for controlling the hydraulic pressure, which can prevent the brake pedal from recoiling when the vehicle is braked. Complete suppression of pedal feedback proves to be disadvantageous, however, if the feedback means is missing so that the driver does not learn that his ABS or anti-skid system has come into play.